THE HISTORY OF THERMAL SPRAYING
From a historical view-point the thermal spraying or metal spraying has got its beginnings in the production of metal powders and was patented for the first time in 1882. Thereby, high-tension gases or vapours were made to escape and liquid metal was poured into the stream of gas (Abb. 1).
This process to produce metal powders was further developed over the course of the next 3 decades. Even though already some porous layers emerged as side products of this production process, no importance was attached to this.
Only the German engineers FRANZ HERKENRATH and FELIX MEYER - both from Aachen - as well as the Swiss engineer M. U. SCHOOP, born in Beulen, tried to take advantage of this characteristic - the production of metal spraying layers. Thus in 1910 the first stationary metal spraying plant was developed.
The disadvantage of this first metal spraying plant (see Abb. 2), which still used liquid metal, was that the component part to be coated had to be led past the plant. Thus the next step was to use fine metal powder as raw material. Thereby, an attempt was made, which is reality today, nearly 100 years later. It was attempted to throw cold metal powder on surfaces in order to achieve layers. At the time this attempt was doomed to failure, however, nowadays this process of "cold gas spraying" or "cold spraying" is available to us as the latest development in the sector of the high-speed coatings.
As it was not possible to introduce cold spraying nearly 100 years ago, the process was developed further and made to what we consider as powder flame spraying today. The next step was the development of coating plants, which could process wires as raw materials. This led to the coating process wire flame spraying.
As it had been achieved that metal spraying had been made a useful procedure with the help of autogenous flames, the next step was the attempt to melt the wires similar to the welding process with the help of an arc. This process is today used as arc spraying.
Continuous further developments resulted in the late 50ies in the detonation spraying, the plasma spraying as well as the laser spraying processes. These processes were first introduced in aviation.
The next step of the development was in the 80ies due to the extension of the plasma spraying process to vacuum plasma spraying and low pressure plasma spraying (VPS/LPPS) as well as the introduction of the high velocity flame spraying (HVOF).
The latest development in the sector of thermal coating is the above-mentioned process of cold spraying.
Since its beginnings in 1948 the company Leistner Hans GmbH has been using thermal coating. The name affix "Süddeutsche Metallspritzwerkstätten" (South German metal spray workshops) is proof of that.